The Effects of Calcium Aluminate Cement Substitution on Physicochemical Properties of Geopolymer–Zeolite Composites

Abstract

Abstract Zeolites are porous aluminosilicate materials and are commonly used as adsorbents for various pollutants. Geopolymers made from industrial waste materials have an aluminosilicate structure similar to zeolites and can be converted to crystalline zeolites under high temperature and pressure conditions (hydrothermal conditions). The present study investigated the effects of fly ash substitution by calcium aluminate cement (CAC) in hydrothermally-treated geopolymer binders (often referred to as geopolymer-zeolite composites or geopolymer-supported zeolites). The substitution levels of fly ash by CAC were varied from 0 to 50% (0, 10%, 20%, 40%, or 50%). A mixture of waterglass and NaOH solutions was used for alkali activation of raw materials. The test results revealed that the CAC significantly affected the strength development and reaction products. All the CAC-substituted specimens showed significantly higher strength than fly ash-based control specimens. It was noted that the rise in compressive strength was mainly due to the formation of C–A–S–H gel in CAC-substituted specimens. The control specimens showed Na–P1 type zeolite while chabazite, faujasite, and hydroxysodalite phases were identified with incorporation of CAC. Hence, it was found that the CAC addition resulted in different Ca/Si molar ratios, which promoted the formation of different types of zeolites, thus these specimens can potentially be used for specific target applications.